Preheat oven to 375 degrees. Line baking sheets with either parchment paper or silicone baking mats.

In the bowl of an electric mixer fitted with a paddle attachment, cream the butter, granulated sugar and brown sugar on medium speed until very light and fluffy, about 5 minutes. Turn the mixer to low and add the eggs, one at a time, mixing until each egg is fully incorporated, scraping down the sides of the bowl with each addition. Add the vanilla extract and mix well.

With the mixer on low, add all but ½ cup of the flour/oat mixture to the butter mixture gradually and mix until just combined. With a large spatula, scrape the sides and bottom of the mixing bowl and make sure everything is well combined. Toss the raisins in with the ½ cup flour/oat mixture and coat the raisins well. Fold into the batter.

Spoon the batter onto the prepared pans using between 1 and 2 tablespoons of batter per cookie, depending on how large you like them, leaving about 2 inches of space between each cookie.

Bake for 12 - 15 minutes or until set and golden brown.

Let cookies cool in the pan for 5 minutes and then transfer to wire racks to finish cooling.